Mechanical screw press

ABSTRACT

A cylindrical cage is lined with spaced screen bars to define a drainage chamber, a screw extends through the chamber and has a plurality of axially spaced worms mounted on a shaft, and axially spaced stationary breaker lugs project inwardly between the flights of the worms. The screw has a recessed conical end surface which mates with a pointed conical end surface of a stationary drainage discharge cone. The discharge cone is supported for axial adjustment by a bearing and a fluid cylinder to vary the size of the annular discharge orifice defined between an orifice ring removably mounted on the cone and a bushing mounted on the frame. The recessed conical surface of the worm and the pointed conical surface on the sleeve cooperate to center the discharge end portion of the screw within the pressing chamber through a layer of compacted material between the surfaces. Each of the worms may also incorporate two diametrically opposed helical flights each extending circumferentially about 170* and which also cooperate to center the screw by balancing the lateral acting forces on the screw.

French et a1.

[52] U.S. Cl 100/117, 100/149, 259/9 [51] Int. Cl B30b 9/14, B30b 9/18[58] Field of Search 100/117, 126, 145-150;

[56] References Cited UNITED STATES PATENTS 3,093,065 6/1963 French..100/150 X 3,285,163 1 1/1966 Burner 100/117 X 3,555,999 1/1971G1owacki.. 100/148 3,225,453 12/1965 Burner 100/117 X 3,400,654 9/1968Vincent.... 100/148 3,411,435 11/1968 French et a1 100/43 3,398,6778/1968 Theobald et a1.... 100/147 X 2,060,408 11/1936 Wood 100/148 UX2,982,990 5/1961 Zomlefer 259/191 3,003,412

Filed:

MECHANICAL SCREW PRESS Inventors: Alfred W. French; Forest J. Starrett,

Jr., both of Piqua, Ohio Assignee: The French Oil Mill MachineryCompany, Piqua, Ohio July 13, 1971 Appl. No.: 162,175

Vincent 100/117 Primary Examiner-John Petrakes Assistant Examiner-PhilipR. Coe Attorney-Jacox & Meckstroth s7 ABSTRACT A cylindrical cage islined with spaced screenbars to define a drainage chamber, a screwextends through the chamber and has a plurality of axially spaced wormsmounted on a shaft, and axially spaced stationary breaker lugs projectinwardly between the flights of the worms. The screw has a recessedconical end surface which mates with a pointed conical end surface of astationary drainage discharge cone. The discharge cone is supported foraxial adjustment by a bearing and a fluid cylinder to vary the size ofthe annular discharge orifice defined between an orifice ring removablymounted on the cone and a bushing mounted on the frame. The recessedconical surface of the worm and the pointed conical surface on thesleeve cooperate to center the discharge end portion of the screw withinthe pressing, chamber through a layer of compacted material between thesurfaces.

. Each of the worms may also incorporate two diametri- 10 Claims, 3Drawing Figures MECHANICAL SCREW PRESS BACKGROUND OF THE INVENTION In amechanical screw press such as disclosed in French et al. U.S. Pat. No.3,411,435, assigned to the assignee of the present invention, the screwincludes a series of axially spaced worms mounted on a shaft, and eachworm has an annular body supporting an integral helical flight. Theworms and flights are spaced axially by collars mounted on the shaft,and a series of stationary breaker lugs project inwardly between thehelical flights to oppose rotation of the pressed material with theworms and thereby assure generally axial flow of the material from eachworm to the next successive worm.

At the discharge end of the press shown in the above patent, the screwshaft projects beyond the final discharge worm and carries a bearingsleeve which projects into a non-rotatable discharge cone. The dischargecone is provided with drainage openings and cooperates with asurrounding annular bushing mounted on the frame to define an annulardischarge orifice. The cone is mounted on the end of a shaft or rodwhich extends from a hydraulic cylinder and is adjustable axially on thescrew shaft to vary the size of the discharge orifice.

When a mechanical screw press such as shown in the above patent, is usedfor expressing moisture from an abrasive material, for example, sugarcane bagasse having abrasive foreign particles such as sand, it has beenfound that the bagasse and foreign particles are forced into theclearance space between the sleeve on the screw shaft and thesurrounding stationary discharge drainage cone, causing the sleeve andcone to wear and substantially increasing the horsepower required todrive the screw. In addition, the replacement of the sleeve and coneresult in substantial maintenance expense. Furthermore, as a result ofthe substantial weight of the discharge end portion of the screw and thehigh pressure lateral forces acting on the screw, it has been difficultto avoid significant wear on the outer surface of the helical flight onthe discharge worm and also on the surrounding screen bars mounted onthe discharge end portion of the cage. That is, these lateral forces areusually sufficient to cause enough deflection of the rotating screwshaft so that the helical flights SUMMARY OF THE INVENTION The presentinvention is directed to a mechanical screw press incorporating improvedmeans for constructing and supporting the screw for significantlyreducing the maintenance required by the press. The invention eliminatesthe need for the long bearing sleeve on the shaft and the resultingmetal to metal contact between the sleeve and the surrounding dischargecone, and provides for retaining the screw in center relation within thepressing chamber so that the wear on the worms and the surroundingscreen bars is substantially reduced. As a result, a screw pressconstructed in accordance with the present invention, may be oper atedcontinuously with less horsepower and for longer periods of time whenhandling abrasive materials. The invention also provides forconveniently removing and replacing at least the final discharge wormafter an extended period of use.

In accordance with one embodiment of the invention, the hollow screwshaft supporting the worms, is cut off inwardly of the discharge end ofthe pressing chamber, and the final discharge worm is retained on theshaft by a plate secured to the shaft by a threaded fastener extendinginto a plug mounted within the shaft. The retaining plate has aninwardly tapering or recessed conical surface, and the final dischargeworm has a frusto-conical end surface which forms a continuation of theconical surface. l

A non-rotatable discharge cone is supported within the discharge end ofthe pressing chamber by a ram or rod extending from a hydrauliccylinder. The discharge cone carries a replaceable orifice ring whichseats on a shoulder formed on the cone and which cooperates physicallycontact the stationary screen bars in the to apply a hard coating on theouter surface of the flight of the discharge worm and to employ'hardenedscreen bars.

Even with the hardened screen bars. and worm flights, when a mechanicalscrew press is used to press sugar cane bagasse which commonly carriessand and other abrasive foreign material, it is occasionally necessaryto stop the screw press, open the split cage and replace the finaldischarge worm on the screw in addition to sometimes replacing thescreen bars adjacent the high pressure discharge end of the press. It isnot uncommon for this replacement to require two or four men from eightto sixteen hours. This results in a substantial ser vice expense and asignificant downtime for the screw press.

with a surrounding stationary frame bushing to define an annulardischarge orifice. The cone also has a conical end surface whichcooperates with the complementary conical surface on the discharge endof the screw to assist in holding the screw in-a concentric or centeredposition within the pressing chamber. When the discharge sleeve isadjusted axially by operation of the hydraulic cylinder to vary the sizeof the discharge orifice, the layer of compacted material confinedbetween the conical surfaces remains substantially uniform in thicknessas a result of the relative rotation of the surfaces. Thus the centeringeffect on the screw is maintained regardless of the spacing between themating conical end surfaces. j

The final discharge worm, and preferably all the worms along the entirelength of the pressing shaft, are constructed with a pair ofdiametrically opposed helical flightseach of which extendscircumferentially approx imately so that there is an approximate l0 gapbetween adjacent ends of the opposing'flights. The two opposed flightson the worms, are effective to balance the lateral forces acting on thescrew and cooperate with the mating conical end surfaces to help centerthe screw within the pressing chamber and thereby minimize lateraldeflection of the screw and rubbing of the worm flights against thesurrounding screen bars.

Other features and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section of thedischarge end portion of a mechanical screw press having a screw shaftassembly and a stationary discharge cone constructed in accordance withthe present invention;

FIG. 2 is an enlarged sectional view of a slightly modified form of thefinal discharge worm; and

FIG. 3 is an axial view of the discharge worm shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the discharge endportion of a screw press which includes a generally cylindrical cagewhich is constructed in two semi-cylindrical mating cage sections 12each having a plurality of parallel spaced arcuate ribs (not shown)integrally connected by longitudinally extending cage members. The cagesections 12 are clamped together by a series of tie bolts (not shown)which extend within the holes 13, and the discharge end of the cage issupported by an upright end wall 14 of the main frame. An axiallyextending tie plate or bar 15 connects the upper end of the wall 14 to amain gear box housing (not shown) located adjacent the opposite or inletend of the cage.

A plurality of axially extending-elongated screen bars 16 are mounted onthe ribs of each cage section 12 and are circumferentially spaced todefine longitudinally extending drainage slots or openings 17therebetween. The screen bars 16 are secured within each cage section byreatining bars 18 to define a cylindrical pressing chamber 20 having aninlet end (not shown) and a discharge end 22 which abuts the framemember 14.

An elongated screw 25 extends through the pressing chamber 20 andincludes a hollow shaft 26 which is connected through a gear box to asuitable drive motor 28. A series of pressure worms, including adischarge worm 29 and a final discharge worm 30, are successivelymounted on the shaft 26 within the pressing chamber 20 and are securedto the shaft by a key 31. The worm 29 includes a generally cylindricalbody 32 and a pair of diametrically opposed integral helical flights 33each of which extend circumferentially around thebody 32 approximately170 as will be explained later in connection with FIGS. 2 and 3.

A series of annular collars 36 are mounted on the shaft 26 interspacedbetween the pressure worms and form gaps or spaces between the worms. Aseries of breaker bars are secured to the retaining bars 18 and includelug portions 38 which project inwardly into the pressing chamber 20 inthe areas of the annular collars '36 and between the worms to minimizerotation of the material being pressed with the screw 25. A finalbreaker bar or lug 39 projects inwardly adjacent the discharge end ofthe final discharge worm 30, and an annular wear bushing 41 surroundsthe flight 33 of the worm 29 to assist in minimizing the wear on thefinal discharge worm and the surrounding screen bars.

The final discharge worm 30 (FIGS. 2 and 3) inv cludes an annular body42 which tapers outwardly toward the discharge end of the screw 25. Apair of diametrically opposed helical flights 44 are formed as anintegral part of the body 42, and each flight extends circumfercntiallyaround the tapered body approximately 170 as mentioned above inconnection with the worm 29. A frusto-conical end surface 45 is formedon the final discharge worm 30 and extends outwardly from a counterbore47. A retaining plate or member 50 seats within the counterbore 47 andincludes a cylindrical portion which projects into the end portion ofthe hollow screw shaft 26. The retaining member 50 is secured to theshaft by a screw 52 which is threaded into a plug 54 welded to the innersurface of the screw shaft 26. The retaining plate 50 has a recessedconical end surface 55 which forms a continuation of the frustoconicalsurface 45 on the worm 30 so that the entire end surface of the screw 25is generally conical.

A large diameter counterbore 59 is formed within the frame member 15 andreceives a hardened stationary discharge ring 60 having a frusto-conicalinner surface 61 which continues inwardly onto a smaller adjacentstationary discharge bushing or ring 62. The discharge rings 60 and 62are retained by an annular plate 64 which is secured to the end framewall 14 by a series of screws 66.

A frame extension member or bracket is rigidly secured to the retainingplate 64 and projects outwardly to support a double acting fluid orhydraulic cylinder 72. The cylinder 72 has a piston rod 74 which isaxially aligned with the screw 25 and is slidably sup ported by abearing 75 mounted on the frame extension member 70 and by a bearing 76mounted on the outer end of a guide tube 77 rigidly secured to frameextension 70. The rod 74 includes an integral spline 78 which engages atubular spline 79 confined within the tube 77 to prevent the rod 74 fromrotating.

A support plate 82 is mounted on the projecting end of the rod 74 andsupports a non-rotatable hollow discharge cone 85 having afrusto-conical portion 86. A cylindrical surface 87 is formed on thecone portion 86 and receives a onepiece orifice ring 88 which seatsagainst a radial shoulder 89. The outer surface of the ring 88cooperates with the inner surface of the surrounding frame bushing 62 todefine an annular discharge orifice 90. An annular array of openings orholes 92 are formed within the cone portion 86 and provide an inwardescape of expressed fluid which drains from the cone 85 through anoutlet 93 formed within the lower portion of the support plate 82. Thesleeve 85 includes a pointed tip portion 94 which has a conical endsurface 95 mating with the conical end surface 55 on the screw 25.

Referring to FIGS. 2 and 3, the worms 29 and 30 are each constructedsimilar to a worm which includes an annular body 102 having a set ofaxially extending threaded holes 103 and an outer frusto-conical surfacetapering outwardly toward the discharge end of the pressing chamber 20.The worm 100 further includes a pair of diametrically opposed helicalflights 104 which are formed as an integral part of the body 102.Preferably, each of the helical flights 104 extends circumferentiallyabout so that opposing ends of the flights 104 define diametricallyopposed axially extending passages or gaps 106 of above 10. The twodiametrically opposed flights 104 cooperate to balance the lateralacting forces on the screw 25 and thus cooperate with the centeringeffect of the conical surfaces 55 and 95 t0 assurethat the discharge endportion of the screw 25 does not sag but remains centered within thepressing chamber 20. The double flights 104 may also be used on thepreceding worms of the screw 25 to provide additional balancing of thelaterally active forces.

When the mechanical screw press is operating for continuously expressingfluid from a material such as sugar cane bagasse, the compressed pulp orbulk material is discharged through the annular orifice 90. Thedischarge cone 85 is positioned axially by actuating the fluid cylinder72 to adjust the area of the orifice 90 according to the back pressuredesired in the pressing chamber 20. Preferably, when the cone 85 and therod 74 are completely extended to obtain the minimum area of thedischarge orifice 90, there is a gap of approximately one-fourth inchbetween the recessed conical end surfaces 45 and 55 on a screw 25 andthe pointed conical end surface 95 on the cone 85.

As a result of the high pressure exerted on the material within thedischarge end portion of the pressing chamber 20, the material flowsinto the gap or space between the surfaces 55 and 95 and the relativerotation between the screw 25 and the cone 85 produces a uniform layerof compacted material within the gap or space. It has been found thatthis layer of material cooperates with the conical surfaces 55 and 95 toeffect centering of the discharge end portion of the screw 25 within thepressing chamber 20.

It has also been found that even when the cone S5 is retracted toincrease the area of the discharge orifice 90, the layer of compactedmaterial between the relative rotating conical surfaces 55 and 95 isstill effective to produce centering of the final discharge worm 30within the chamber 20. For example, when the space between the conicalsurfaces 55 and 95 is upwards to 2% inches, the compacted layer ofmaterial between the surfaces is still effective to hold the axis of thescrew 25 in alignment with the axis of the sleeve 85 and cylinder rod74.

In summary, it is apparent that a mechanical screw press constructed inaccordance with the present invention, provides desirable features andadvantages. For example, the invention eliminates the long bearingsleeve on the screw shaft as shown in the above patent and therebyeliminates the resulting wear problem and the additional power requiredto drive the screw. Furthermore, the generally conical end surface 55 onthe screw 25 cooperates with the pointed generally conical end surface95 on the stationary discharge cone 85 to produce self-centering forceson the discharge end portion of the screw. These self-centering forcesremain effective even though the non-rotating discharge cone 85 isadjusted axially and the, space between the surfaces 55 and 95 changes.As a result, when the screw press is operating to express moisture froma material containing abrasive foreign particles such as sugar canebagasse containing sand, the wear on the outer surface of the flight 44and on thesurrounding screen bars 16, is significantly reduced.

Furthermore, when the worms are constructed as shown in FIG. 2 and 3,the diametrically opposed helical flights of less 180, cooperate withthe conical surfaces 55 and 95 to help in centering the screw within thepressing chamber 20. By balancing the lateral acting forces on thescrew. It is also apparent that the double flighted worms may beconveniently removed and replaced by new worms. To accomplish this, thehydraulic cylinder 72 is actuated to retract the nonrotating dischargecone 85, after which the cone is removed from the support plate 82. .Theworm retaining plate 50 is then removed from the end of the screw shaft26, and the final discharge worm 3th is pulled from the shaft 26 simplyby extending pull bolts through axially extending holes within thesupport plate 82 and threading the pull bolts into the holes 103 withinthe discharge worm. When the rod 74 and support plate 82 are retracted,the final discharge worm 100 is pulled from the screw shaft 26. Beforethe worm is pulled, however, one of the gaps 106 is aligned with thefinal breaker lug 39 by rotating the screw.

It is also apparent that the minimum size of the orifice 90 may beconveniently changed simply by retracting the cone 85 and replacing theorifice ring 88 with another ring having a greater or lesser outerdiameter. Previously, it was necessary to interchange either the entirecones or the frame bushings 62 to change the minimum size of theorifice. This was an expensive and time consuming operation.

While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. A mechanical screw press for expressing fluid from a material,comprising means defining an elongated pressing chamber having an inletand an outlet, an elongated rotatable screw extending within saidchamber and including a shaft, a series of worms mounted on said shaft,each of said worms having at least one outwardly projecting helicalflight, means for rotating said screw, means for compressing materialwithin said chamber as the material moves toward said outlet in responseto rotationof said screw, a retaining member connected to said shaft forretaining the final said worm on said shaft, said retaining memberforming a gener ally conical end surface on the discharge end portion ofsaid screw within said chamber, a cone member positioned within saidoutlet and projecting into said chamber, a generally frustoconicalsurface on said cone member and having drainage means therein, means forsupporting said cone member concentrically within said outlet and saidpressing chamber, said cone member cooperating with said outlet todefine an annular discharge orifice, means forming a generally conicalend surface on said cone member adjacent said end surface of said screw,and said end surface of said cone member cooperating with said endsurface of said screw and the material compressed therebetween to effectsubstantial centering of said discharge end portion A of said screwwithin said chamber. a

2. Amechanical screw press for expressing fluid from .a material,comprising means defining an elongated pressing chamber having inlet andan outlet, an elongated rotatable screw extending within said chamberand including a shaft, a series of worms mounted on said shaft, each ofsaid worms having at least one out- 1 wardly projecting helical flight,means for rotating said screw, means for compressing material withinsaid 1 chamber as the material moves toward said outlet in response torotation of said screw, said screw having a ta- 7 member axially withinsaid discharge end portion of said chamber.

i 3. A mechanical screw press for expressing fluid from a material,comprising means defining an elongated pressing chamber with an inletand an outlet, an elongated rotatable screw extending through saidchamber and including a shaft, a series of worms mounted on said shaft,each of said'worms having at least one outwardly projecting helicalflight, means for rotating said screw, means for compressing materialwithin said chamber as the material moves toward said outlet in responseto rotation of said screw, a cone member positioned within said outletin axial alignment with said screw, means for moving said cone memberaxially, a rigid orifice ring mounted on said cone member andcooperating with said outlet to define an annular discharge orifice,means forming an annular seat on said cone member for positioning saidorifice ring, and said orifice ring being removable from said seat toprovide for replacing said orifice ring.

4. A mechanical screw press for expressingfluid from a material,comprising means defining an elongated pressingchamber having an inletand an outlet, an elongated rotatable screw extending within saidchamber and including a shaft, a series of worms mounted on said shaft,each of said worms having at least one outwardly projecting helicalflight, means forrotating said screw, means for compressing materialwithin said chamber as the material moves toward said outlet in responseto rotation of said screw, a retaining member connected to said shaftfor retaining the final said worm on said shaft, said retaining memberforming a generally conical end surface on the discharge end portion ofsaid screw within said chamber, a cone member positioned within saidoutlet and projecting into said chamber, means for supporting said conemember concentrically within said outlet and said pressing chamber, anorifice ring mounted on said cone member and coopervating with saidoutlet means to define an annular discharge orifice, said orifice ringbeing removable from said cone member to provide for convenientlyreplacing said orifice ring, means forming a generally conical endsurface on said cone member adjacent said end surface of said screw, andsaid end surface of said cone member cooperating with said end surfaceof said screw and the material compressed therebetween to effectsubstantial centering of said discharge end portion of said screw withinsaid chamber.

5. A mechanical screw press for expressing fluid from a material,comprising means. defining an elongaged pressing chamber having an inletand an outlet, an

elongated rotatable screw extending within said chamber and including ashaft, a series of worms mounted on said shaft, each of said wormshaving at least one outwardly projecting helical flight, means forrotating said screw, means for compressing material within said chamberas the material moves toward said outlet in response to rotation of saidscrew, at least the final discharge worm includes a pair ofdiametrically opposed said flights each extending circumferentially nogreater than 180, a retaining member connected to said shaft forretaining the final said worm on said shaft, said retaining memberforming a generally conical end surface on the discharge end portion ofsaid screw within said chamber, a cone member positioned within saidoutlet and projecting into said chamber, means for supporting said conemember concentrically within said outlet and said pressing chamber, saidcone member cooperating with said outlet to define an annular dischargeorifice, means forming a generally conical end surface on said conemember adjacent said end surface of said screw, and said end surface ofsaid cone member cooperating with said end surface of said screw and thematerial compressed therebetween to effect substantial centering of saiddischarge end portion of said screw within said chamber.

6. A screw press as defined in claim 2 wherein said cone member includesa hollow portion having a frustoconical outer surface, means definingdrainage openings within said frustoconical surface, a tip memberrigidly secured to said hollow member, and said tip member having apointed said generally conical end surface.

7. A screw press as defined in claim 1 wherein at least the finaldischarge worm including a pair of diametrically opposed said flights,and each of the latter said flights extends circumferentiallyapproximately 8.'A press as defined in claim 2 including a retainingmember mounted on the discharge end of said shaft and having means forsecuring the final discharge worm to said shaft, and said retainingmember having a generally conical said end surface.

9. A press as defined in claim 1 comprising a hollow said shaft, a plugmember mounted within the discharge end portion of said hollow shaft,and a threaded fastener securing said retaining member to said plugmember.

10. A screw press as defined in claim 3 wherein said seat comprises ashouldered outer surface on said cone member, and said orifice ring isseated on said outer

1. A mechanical screw press for expressing fluid from a material,comprising means defining an elongated preSsing chamber having an inletand an outlet, an elongated rotatable screw extending within saidchamber and including a shaft, a series of worms mounted on said shaft,each of said worms having at least one outwardly projecting helicalflight, means for rotating said screw, means for compressing materialwithin said chamber as the material moves toward said outlet in responseto rotation of said screw, a retaining member connected to said shaftfor retaining the final said worm on said shaft, said retaining memberforming a generally conical end surface on the discharge end portion ofsaid screw within said chamber, a cone member positioned within saidoutlet and projecting into said chamber, a generally frustoconicalsurface on said cone member and having drainage means therein, means forsupporting said cone member concentrically within said outlet and saidpressing chamber, said cone member cooperating with said outlet todefine an annular discharge orifice, means forming a generally conicalend surface on said cone member adjacent said end surface of said screw,and said end surface of said cone member cooperating with said endsurface of said screw and the material compressed therebetween to effectsubstantial centering of said discharge end portion of said screw withinsaid chamber.
 2. A mechanical screw press for expressing fluid from amaterial, comprising means defining an elongated pressing chamber havinginlet and an outlet, an elongated rotatable screw extending within saidchamber and including a shaft, a series of worms mounted on said shaft,each of said worms having at least one outwardly projecting helicalflight, means for rotating said screw, means for compressing materialwithin said chamber as the material moves toward said outlet in responseto rotation of said screw, said screw having a tapered end surfaceterminating within said chamber inwardly of said outlet, a hollow conemember projecting into the discharge end portion of said chamber andhaving a tapered end surface opposing said end surface of said screw,means for supporting said cone member concentrically within said outletand said pressing chamber, means on said cone member cooperating withsaid outlet to define an annular discharge orifice, means definingdrainage openings within said cone member between said end surface ofsaid screw and said discharge orifice, and means for moving said conemember axially within said discharge end portion of said chamber.
 3. Amechanical screw press for expressing fluid from a material, comprisingmeans defining an elongated pressing chamber with an inlet and anoutlet, an elongated rotatable screw extending through said chamber andincluding a shaft, a series of worms mounted on said shaft, each of saidworms having at least one outwardly projecting helical flight, means forrotating said screw, means for compressing material within said chamberas the material moves toward said outlet in response to rotation of saidscrew, a cone member positioned within said outlet in axial alignmentwith said screw, means for moving said cone member axially, a rigidorifice ring mounted on said cone member and cooperating with saidoutlet to define an annular discharge orifice, means forming an annularseat on said cone member for positioning said orifice ring, and saidorifice ring being removable from said seat to provide for replacingsaid orifice ring.
 4. A mechanical screw press for expressing fluid froma material, comprising means defining an elongated pressing chamberhaving an inlet and an outlet, an elongated rotatable screw extendingwithin said chamber and including a shaft, a series of worms mounted onsaid shaft, each of said worms having at least one outwardly projectinghelical flight, means for rotating said screw, means for compressingmaterial within said chamber as the material moves toward said outlet inresponse to rotation of said screw, a retaining member connected to saidshaft for retaining the final said worm on said shaft, said retAiningmember forming a generally conical end surface on the discharge endportion of said screw within said chamber, a cone member positionedwithin said outlet and projecting into said chamber, means forsupporting said cone member concentrically within said outlet and saidpressing chamber, an orifice ring mounted on said cone member andcooperating with said outlet means to define an annular dischargeorifice, said orifice ring being removable from said cone member toprovide for conveniently replacing said orifice ring, means forming agenerally conical end surface on said cone member adjacent said endsurface of said screw, and said end surface of said cone membercooperating with said end surface of said screw and the materialcompressed therebetween to effect substantial centering of saiddischarge end portion of said screw within said chamber.
 5. A mechanicalscrew press for expressing fluid from a material, comprising meansdefining an elongaged pressing chamber having an inlet and an outlet, anelongated rotatable screw extending within said chamber and including ashaft, a series of worms mounted on said shaft, each of said wormshaving at least one outwardly projecting helical flight, means forrotating said screw, means for compressing material within said chamberas the material moves toward said outlet in response to rotation of saidscrew, at least the final discharge worm includes a pair ofdiametrically opposed said flights each extending circumferentially nogreater than 180*, a retaining member connected to said shaft forretaining the final said worm on said shaft, said retaining memberforming a generally conical end surface on the discharge end portion ofsaid screw within said chamber, a cone member positioned within saidoutlet and projecting into said chamber, means for supporting said conemember concentrically within said outlet and said pressing chamber, saidcone member cooperating with said outlet to define an annular dischargeorifice, means forming a generally conical end surface on said conemember adjacent said end surface of said screw, and said end surface ofsaid cone member cooperating with said end surface of said screw and thematerial compressed therebetween to effect substantial centering of saiddischarge end portion of said screw within said chamber.
 6. A screwpress as defined in claim 2 wherein said cone member includes a hollowportion having a frustoconical outer surface, means defining drainageopenings within said frustoconical surface, a tip member rigidly securedto said hollow member, and said tip member having a pointed saidgenerally conical end surface.
 7. A screw press as defined in claim 1wherein at least the final discharge worm including a pair ofdiametrically opposed said flights, and each of the latter said flightsextends circumferentially approximately 170*.
 8. A press as defined inclaim 2 including a retaining member mounted on the discharge end ofsaid shaft and having means for securing the final discharge worm tosaid shaft, and said retaining member having a generally conical saidend surface.
 9. A press as defined in claim 1 comprising a hollow saidshaft, a plug member mounted within the discharge end portion of saidhollow shaft, and a threaded fastener securing said retaining member tosaid plug member.
 10. A screw press as defined in claim 3 wherein saidseat comprises a shouldered outer surface on said cone member, and saidorifice ring is seated on said outer surface.